Tandem utilization of CO2 photoreduction products for the carbonylation of aryl iodides

Photocatalytic CO2 reduction reaction has been developed as an effective strategy to convert CO2 into reusable chemicals. However, the reduction products of this reaction are often of low utilization value. Herein, we effectively connect photocatalytic CO2 reduction and amino carbonylation reactions in series to reconvert inexpensive photoreduction product CO into value-added and easily isolated fine chemicals. In this tandem transformation system, we synthesize an efficient photocatalyst, NNU-55-Ni, which is transformed into nanosheets (NNU-55-Ni-NS) in situ to improve the photocatalytic CO2-to-CO activity significantly. After that, CO serving as reactant is further reconverted into organic molecules through the coupled carbonylation reactions. Especially in the carbonylation reaction of diethyltoluamide synthesis, CO conversion reaches up to 85%. Meanwhile, this tandem transformation also provides a simple and low-cost method for the 13C isotopically labeled organic molecules. This work represents an important and feasible pathway for the subsequent separation and application of CO2 photoreduction product.

To further explore the excitation properties of the system, we perform time-dependent DFT (TDDFT) calculations with 50 low-lying excitations, which computes the signatures of electronically excited states and simulates the UV-vis spectra. As shown in Supplementary Fig. 26, the calculation results agree well with the experiments, suggesting the reliability of the computation methods and models. In the following, electron excitation analysis is performed to characterize the absorption peaks with the help of Multiwfn, and three low-lying excitations with the strongest excitation intensities are selected. Supplementary Fig. 27 illustrates the charge density difference between the ground state and the excited state, and the photo-excited electrons are marked as red while the holes are denoted as blue. It can be noted the Ni centers serve as electron donors and the surrounding ligands accept the photo-excited electrons for the three selected excitations, and we attribute these excitations to MLCT. Granted, the excitations in the UV-vis regime can be very complicated and involve many kinds of change transfer processes. However, we can conclude here, based on the calculation results and analysis, that the observed peaks around 400-800 nm are mainly dominated by MLCT. Figure 28. When NNU-55-Ni or NNU-55-Ni-NS were used in the photocatalytic CO2RR as starting catalyst, a function of the irradiation time of CO production from CO2 photoreduction.

Supplementary
When NNU-55-Ni-NS was used as catalyst to complete photocatalytic CO2RR, the CO product formation rate is significantly higher than that of the bulky NNU-55-Ni, especially in the initial stage of the reaction.   We measured the UV-vis absorption spectra of a pure Ru solution and a Ru solution containing NNU-55-Ni-NS catalyst (Supplementary Figure 32). The results revealed that the addition of catalyst has almost no effect on the inherent light absorption of [Ru(bpy)3]Cl2 (PS). And the steady-state photoluminescence (PL) spectroscopy of the Ru solution containing different masses of NNU-55-Ni-NS catalysts is characterized (without TEOA), in which the PL intensity of [Ru(bpy)3]Cl2 decrease as the increased catalyst concentration (Fig. 3g). The above two experiments confirmed that the quenching of the PL intensity is attributed to the photoexcited electrons transferred from the Ru photosensitizer to the catalyst. We also tested the UV/vis absorption spectrum changes of

Supplementary Tables
Supplementary Table 1. Crystal data and structure refinement for NNU-55-Co.

Complexes
NNU-55-Co formula C28H19Co3N12O6 fw 796.34 crystal system tetragonal The average lifetime was calculated by using the equation: The time-resolved fluorescence decay spectrum was fitted using the E-exponential model：

Supplementary Note 2: Single-Crystal X-ray Analyses.
The single-crystal diffraction analysis of compound NNU-55-Co was collected on Bruker APEX Duo II equipment CCD area detector at 296 K. The X-ray generator was  Table S1.

Supplementary Note 3: Calculational Methods.
The calculations were performed using the ORCA package employing the resolution of identity approximation 5 . All the DFT calculations were performed using the hybrid B3LYP functional. Basis sets of def2-TZVP 6 were adopted for all atoms in the complexes with where h, v and KB are Planck constant, vibrational frequencies and Boltzmann constant, respectively.

Supplementary Note 4: Electrochemical Measurements.
Preparation of the working electrode. and Morlet function with κ=10, σ=1 was used as the mother wavelet to provide the overall distribution.

Supplementary Note 6: Apparent Quantum Efficiency (AQE).
The AQE was calculated as follow: = (2 × the number of product) molecules produces the number of incident photons Fluorescence intensity was then evaluated.

Photoluminescence lifetime experiments.
The samples were excited by the incident light of 390 nm and the PL decay spectra at 605 nm are monitored using PICOQuant FT-300 spectrofluorometer. These solution systems were bubbled with CO2 for 30 min to dissolve oxygen and maintain saturated conditions.
The mixed solution contained acetonitrile (10 mL) and deionized water (100 μL). Then The yield of these isolated products was also isolated by silica gel chromatography.
Mass spectrum and standard curve of all products.      There is no alert level A and B error.